Scrapy comes with a built-in telnet console for inspecting and controlling a
Scrapy running process. The telnet console is just a regular python shell
running inside the Scrapy process, so you can do literally anything from it.

Sent just before the telnet console is opened. You can hook up to this
signal to add, remove or update the variables that will be available in the
telnet local namespace. In order to do that, you need to update the
telnet_vars dict in your handler.